STABILITY OF DOMOIC ACID UNDER VARIOUS STORAGE CONDITIONS

Keri Baugh, Kathi A. Lefebvre, John C. Wekell, and Vera L. Trainer

NOAA Fisheries, Marine Biotoxins Program, Northwest Fisheries Science Center, Seattle, WA 98112, USA

Harmful algal bloom researchers often collect phytoplankton samples during multi-day research cruises and frequently need to store these samples for later toxin analysis. In order to obtain accurate measurements and avoid the confounding effects of toxin degradation, proper storage procedures must be defined and used. To this end, the present study examined the stability of the water soluble algal toxin, domoic acid (DA), under various storage conditions using both a certified reference standard prepared in filtered seawater and field-collected seawater samples. Filtered seawater (0.45µm) was spiked with a purified DA reference standard (DACs-1C) and 1 ml aliquots were stored in sealed glass HPLC vials in both the light and dark at room temperature and at 4ºC. The same samples were stored at -20ºC and -80ºC in the dark. Samples preserved with 10% methanol were also examined using each storage condition. DA was quantified using HPLC-UV methods in aliquots from each treatment stored for various periods of time. Additionally, to determine appropriate storage conditions for field-collected phytoplankton samples, filtered particulate DA samples collected during a Pseudo-nitzschia bloom in September, 2004, were sub-sampled and stored at room temperature in the light and dark as well as at 4ºC and -20ºC, in the dark only. DA was measured at several time periods during the 6-month storage treatment. In general, DA was relatively stable during long-term storage with minor influences by light and temperature. However, DA levels in room temperature and -4°C treatments were significantly affected by evaporation, which caused an apparent increase in DA concentration over time. Although toxin increases due to evaporation can be easily corrected by accounting for volume loss, the prevention of evaporation using appropriate sized and tightly-sealed containers is preferable. Recommendations for proper storage of DA samples will be discussed.